Method for locating, via ultra high frequency, a mobile device for “hands-free” access to an automotive vehicle and associated locating device

The invention relates to a method for locating, via ultra high frequency, a mobile device for “hands-free” access to an automotive vehicle and an associated locating device that is on board the vehicle.

The invention applies more particularly to systems for “hands-free” access to automotive vehicles. A system for access, referred to as “hands-free” access, to an automotive vehicle allows an authorized user to lock and/or unlock the openings of his or her vehicle without using a key. For this, the vehicle identifies a badge or remote control carried by the user and if the badge or remote control is identified as belonging to the vehicle, then the vehicle locks or unlocks its openings.

This “hands-free” access system is known to a person skilled in the art. It is generally composed of an electronic control unit on board the vehicle, one or more radiofrequency (RF) antennas located on the vehicle and an identification badge or remote control comprising an RF antenna carried by the user.

An identifier exchange between the badge and the vehicle via RF antennas allows the badge to be identified by the vehicle and locking or unlocking to be triggered by the latter.

The identifier may be contained within a portable device other than a badge or a remote control, e.g. it may be contained within a cell phone or a watch worn by the user.

The identifier exchange is generally carried out via radiofrequency (RF) waves and by low frequency (LF) waves. The vehicle first transmits, via the LF antennas, an LF interrogation signal and the badge, if it is located within the reception area of said signal, sends an RF presence message containing its identifier back to the vehicle.

The precise location of the badge around the vehicle is carried out by measuring the intensity of the LF signal, originating from the vehicle, received by the badge (via the antennas and the electronic control unit), which measurements are more commonly known as RSSI (“received signal strength indication” measurements, or measuring the power of a signal received by an antenna on reception). The measurement of the power of the signal, originating from each LF antenna, received by the badge is analyzed by a locating device on board the vehicle, which thereby determines the position of the badge with respect to said LF antennas, i.e. with respect to the vehicle.

To this end, the locating device D of the prior art comprises, as shown in FIG. 1 , an electrical power supply source Vcc supplying power to a transceiver 10 that is electrically connected to at least one antenna A via an electrical line 20 .

The locating device D generally comprises three to four antennas A.

This RSSI measurement allows the badge to be precisely located around and inside the vehicle in order to allow the openings to be locked/unlocked, and also the vehicle to be started, once the badge is detected inside the vehicle.

Mobile devices, e.g. cell phones, are now increasingly equipped with the Bluetooth® or Bluetooth Low Energy “BLE” communication standard, i.e. ultra high frequency (UHF) communication from 2400 MHz to 2480 MHz. This communication standard has the advantage of being universal and therefore requires no country-specific homologation (only international Bluetooth Low Energy certification), as is the case with current RF/LF communication standards whose operating frequencies vary according to the country.

It therefore becomes necessary to adapt the hands-free access system so that it may also operate with the Bluetooth® communication standard and no longer only via radio- and low frequency (RF/LF) waves.

The advantage of the Bluetooth® communication standard is that it allows a long communication range of approximately 250 m around the vehicle. However, it does not allow the presence of the mobile device to be detected at shorter distances. For example, when the mobile device is located at tens of centimeters from the vehicle and the user wishes to unlock his or her vehicle, which was possible with the communication device of the prior art operating over an exchange of RF and LF waves. Specifically, the RSSI measurement of a Bluetooth signal is very imprecise and varies greatly depending on the environment (noise, disruptions) and it is not possible to know if the device is at 5 m, 10 m, 40 m or more.

Nor is it therefore possible to start the vehicle by using Bluetooth® communication, as starting is only authorized when the mobile device is located inside the vehicle and within a few centimeters of the UHF antennas of the vehicle. However, given the long range of Bluetooth®, the detection of said mobile device within a few centimeters of the UHF antennas is not possible.

The invention proposes an ultra high frequency device for locating the mobile device allowing these drawbacks to be overcome.

More specifically, the ultra high frequency locating device according to the invention allows the presence of the mobile device to be detected at multiple distances around the vehicle, from a few centimeters to multiple meters, as well as at a few centimeters from the UHF antennas on board the vehicle, thereby making “hands-free” starting possible with the Bluetooth® communication standard, which was not possible in the prior art with said communication standard.

Other features and advantages of the invention will become apparent upon reading the description that will follow and upon examining the appended drawings in which:

FIG. 1 , explained above, diagrammatically shows the locating device D according to the prior art;

FIG. 2 diagrammatically shows the locating device D′ according to the invention;

FIGS. 3 a -3 c diagrammatically show the areas for locating the mobile device around the vehicle, according to the invention;

FIG. 4 shows the locating device D′ in a vehicle, according to the invention; and

FIG. 5 shows a graphical representative of the attenuation of UHF waves in decibels (dBi) according to distance (Li).

The locating device D′ according to the invention is illustrated in FIG. 2 . The locating device D′ comprises:

an electrical source Vcc; an ultra high frequency transceiver, more specifically a Bluetooth® transceiver 10 ′, comprising a printed circuit board; an antenna A′.

According to the invention, said locating device D′ additionally comprises, between the transceiver 10 ′ and the antenna A′, i.e. on the (transmission/reception) electrical communication line 20 ′ between the transceiver 10 ′ and the antenna A′, at least one attenuation module M 1 . Said locating device D′ also comprises means 30 for controlling the attenuation module M 1 and means for determining the location of the mobile device 40 .

In FIG. 2 , a plurality of attenuation modules located, in series, on the communication line 20 ′ are shown: a first attenuation module M 1 , a second attenuation module M 2 and a third attenuation module M 3 . As shown in FIG. 2 , the locating device D′ also comprises:

means 30 for controlling the plurality of attenuation modules M 1 , M 2 , M 3 , that are integrated, for example, in the transceiver 10 ′, as well as means for determining the location of the mobile device 40 that are electrically connected to the transceiver 10 ′ and to the means 30 for controlling the attenuation module.

Each attenuation module, the first attenuation module M 1 , the second attenuation module M 2 or the third attenuation module M 3 , is located at a predetermined distance from the transceiver 10 ′, in this instance at a first distance L 1 , a second distance L 2 and a third distance L 3 , respectively.

Each attenuation module, the first attenuation module M 1 , the second attenuation module M 2 or the third attenuation module M 3 , also comprises:

a switching means, e.g. a switch, a first switch S 1 , a second switch S 2 and a third switch S 3 , respectively, and an impedance, a first impedance Z 1 , a second impedance Z 2 and a third impedance Z 3 , respectively, each impedance, the first impedance Z 1 , the second impedance Z 2 or the third impedance Z 3 , having a predetermined value and being electrically connected to ground.

In one preferred embodiment of the invention, the predetermined values of the first impedance Z 1 , the second impedance Z 2 or the third impedance are all mutually equal and are between 0 and 100 kΩ, for example said impedances each have a value of 50Ω.

For each attenuation module, for the first attenuation module M 1 , for the second attenuation module M 2 and for the third attenuation module M 3 , each switching means, i.e.: the first switch S 1 , the second switch S 2 or the third switch S 3 , may be activated by the control means 30 in order to select one of the two following positions:

a first position in which the transceiver 10 ′ or the preceding attenuation module (M 1 , M 2 ) is disconnected from the antenna A′ or from the subsequent attenuation module (M 2 , M 3 ) and in which the transceiver 10 ′ or the preceding attenuation module is electrically connected to the impedance (Z 1 , Z 2 , Z 3 ) associated with said switching means; a second position in which the switching means S 1 , S 2 , S 3 electrically connects the transceiver 10 ′ or the preceding attenuation module M 1 , M 2 to the antenna A′ or to the subsequent attenuation module M 2 , M 3 .

Each switching means (the first switch S 1 , the second switch S 2 or the third switch S 3 ) therefore allows the transceiver 10 ′ to be disconnected from the antenna A′ and the transceiver 10 ′ to be connected to an associated attenuation module (to the first attenuation module M 1 , to the second attenuation module M 2 or to the third attenuation module M 3 ), i.e. the transceiver 10 ′ to be connected to an impedance (to the first impedance Z 1 , to the second impedance Z 2 or to the third impedance Z 3 ) that is electrically connected to ground, has a predetermined value and is located at a predetermined distance (at a first distance L 1 , a second distance L 2 and a third distance L 3 , respectively) from said transceiver 10 ′.

For example, in FIG. 3 a , the first switch S 1 is in the first position and it electrically connects the transceiver 10 ′ to the first impedance Z 1 of the first attenuation module M 1 that is located at a first distance L 1 from the transceiver 10 ′. In this first configuration, the transceiver 10 ′ transmits an ultra high frequency signal, this signal is propagated through the printed circuit board of said transceiver 10 ′ and makes the printed circuit board resonate at said frequency. The UHF signal is also propagated through the communication line 20 ′ up to the first impedance Z 1 and then to ground. The maximum range of the UHF waves thus generated by the locating device D′ depends on the first predetermined distance L 1 between the first attenuation module M 1 and the transceiver 10 ′, as well as on the predetermined value of the first impedance Z 1 . In this first configuration, the first distance L 1 and the value of the first impedance Z 1 are chosen in such a way that the range of the UHF waves thus transmitted is limited to a first locating area A 1 that is located within the vehicle V (cf. FIG. 4 ).

In FIG. 3 b , the first switch S 1 is in the second position and it electrically connects the transceiver 10 ′ to the second attenuation module M 2 . As for the second switch S 2 , it is in the first position and it electrically connects the first attenuation module M 1 , itself connected to the transceiver 10 ′, to the second impedance Z 2 , located at a second distance L 2 from the transceiver 10 ′.

In this example, the value of the second impedance Z 2 is equal to the value of the first impedance Z 1 , and the second distance L 2 is greater than the first distance L 1 .

In this second configuration of the locating device D′ of the invention, the range of the UHF waves thus transmitted is longer than that of the first configuration and defines an outside area close to the vehicle V which will be referred to as the second locating area A 2 ; said second locating area A 2 is centered on the vehicle, is larger than the first locating area A 1 and covers the first locating area A 1 (cf. FIG. 4 ).

In FIG. 3 c , the first switch S 1 and the second switch S 2 are in the second position. The second switch S 2 electrically connects the second attenuation module M 2 , itself electrically connected to the transceiver 10 ′ via the first switch, to the third impedance Z 3 . The third switch S 3 is in the first position and it electrically connects the second attenuation module M 2 (i.e. the transceiver 10 ′) to the third impedance Z 3 , located at a third distance L 3 from the transceiver 10 ′.

In this example, the value of the third impedance Z 3 is equal to the value of the second impedance Z 2 , and the third distance L 3 is greater than the second distance L 2 .

In this third configuration of the locating device D′ of the invention, the range of the UHF waves thus transmitted is longer than that of the second configuration and defines a third locating area A 3 , i.e. an area centered on the vehicle, larger than the second locating area A 2 and covering the first and second locating areas A 1 and A 2 (cf. FIG. 4 ).

Of course, a fourth configuration consists of flipping all of the switches (S 1 , S 2 , S 3 ) to the second position, in which case the transceiver 10 ′ is connected to the antenna A′ and the transmission range of the locating device D′ is at maximum, equal to the range of Bluetooth®.

Of course, the values of the first, second and third impedances Z 1 , Z 2 , Z 3 may be different to one another depending on the desired dimensions of the locating areas.

In FIG. 4 , solely by way of example, a mobile device (T), e.g. a cell phone, is located within the third locating area A 3 .

When the locating device D′ is in the third configuration and transmits an identification request via UHF waves, the mobile device (T) located in the third locating area A 3 receives the identification request originating from the transceiver 10 ′ and in turn sends its identifier back to said transceiver 10 ′.

The identifier received by the transceiver is transmitted to the means for determining the location 40 of the mobile device T. As said determining means 40 are connected to the control means 30 , said determining means receive information regarding the configuration of the locating device D′, more particularly the position of the switching means and consequently the targeted locating area, in this case the third locating area A 3 . If the received identifier is validated (if it corresponds to an identifier of a mobile device T that is paired with the vehicle V) then said locating means 40 deduce that the mobile device T is present in the third locating area A 3 .

The control means 30 , the transceiver 10 ′ and the determining means 40 may be software means that are integrated in a control unit (not shown) of BCM (body control module) type.

FIG. 5 is a graphical representation of the attenuation of the UHF waves in decibels (dBi) according to each distance (Li), the first distance L 1 , the second distance L 2 or the third distance L 3 (between the transceiver 10 ′ and the first attenuation module M 1 , the second attenuation module M 2 or the third attenuation module M 3 ). Each distance (L 1 , L 2 , L 3 ) corresponds to an attenuation of the UHF waves (dB 1 , dB 2 , dB 3 ) and a locating area (A 1 , A 2 , A 3 ) of the mobile device.

The attenuation dBi of the UHF waves according to the distance Li is given by the following formula:

DBi=A ×ln( Li )+ B

or equally:

Li = e ( ( DBi - B ) A )

where:

Li: predetermined distance

DBi: attenuation in decibels

A: coefficient greater than zero

f: transmission frequency

ε PCB : the relative permittivity of the printed circuit board of the locating device D′

ε AIR : the permittivity of air

C: celerity.

The first distance L 1 corresponds to a first strong attenuation dB 1 of the range of the transmitted UHF waves and therefore a first locating area A 1 .

The second distance L 2 corresponds to a second attenuation dB 2 , weaker than the first attenuation, defining a second locating area A 2 that is larger than the first locating area A 1 .

The third distance L 3 corresponds to a weak attenuation dB 3 of the range of the waves and therefore a third locating area A 3 that is larger than the second locating area A 2 .

We therefore have:

A 1< A 2< A 3

and:

L 1< L 2< L 3

with:

Z 1= Z 2= Z 3

For example, if Z 1 =Z 2 =Z 3 =50Ω,

and by making:

L 1 =2 mm

L 2 =10 mm

L 3 =30 mm

then the maximum range of the UHF waves for each locating area is approximately equal to:

The range of the first locating area A 1 is equal to 1 meter.

The range of the first locating area A 2 is equal to 5 meters.

The range of the first locating area A 3 is equal to 10 meters.

The locating device D′ of the invention therefore allows the mobile device T to be located, via ultra high frequency waves, i.e. via Bluetooth®, in at least one locating area A 1 by disconnecting the transceiver 10 ′ from the antenna A′ and by connecting said transceiver 10 ′ to an attenuation module (M 1 , M 2 or M 3 ) located at a predetermined distance (L 1 , L 2 or L 3 ) from the transceiver 10 ′ and comprising an impedance (Z 1 , Z 2 , Z 3 ) of predetermined value connected to ground. The predetermined distance (L 1 , L 2 , L 3 ) between the transceiver 10 ′ and the attenuation module M 1 , M 2 , or M 3 , along with the predetermined value of the impedance Z 1 , Z 2 , Z 3 , define an area A 1 , A 2 , A 3 for locating the mobile device T around the vehicle V.

In one preferred embodiment, the locating device D′ comprises a plurality of attenuation modules M 1 , M 2 , M 3 .

In this preferred embodiment, the plurality of attenuation modules M 1 , M 2 , M 3 allows the predetermined distance between the transceiver 10 ′ and the attenuation module (M 1 , M 2 , M 3 ) and/or the predetermined value of the impedance Z 1 , Z 2 , Z 3 to be made to vary in order to define multiple areas A 1 , A 2 , A 3 for locating the mobile device T around the vehicle V, i.e. multiple UHF wave transmission areas with different dimensions in order to precisely locate the mobile device T around or inside the vehicle V.

The invention therefore ingeniously allows the range of the ultra high frequency (Bluetooth®) waves to be “downgraded” from a maximum range in the prior art of 250 m to roughly a few centimeters, in order to precisely define areas for locating a mobile device T inside and around a vehicle V. With the locating method of the invention, locating a mobile device inside a vehicle via Bluetooth® in order to authorize “hands-free” starting is now possible.